Gem-Knight Ruby

"Gem-Knight Garnet" + 1 "Gem-Knight" monster Must first be Fusion Summoned with the above Fusion Materials. Once per turn: You can Tribute 1 other face-up "Gem-" monster; this card gains ATK equal to the ATK that Tributed monster had on the field, until the end of this turn. If this card attacks a Defense Position monster, inflict piercing battle damage to your opponent.